Yirrkala omanensis ( Norman, 1939 )

Hibino, Yusuke & Ho, Hsuan-Ching, 2024, Species of the snake eel genus Yirrkala Whitley, 1940 from Taiwan, with descriptions of a new species and two new records (Anguilliformes, Ophichthidae), ZooKeys 1220, pp. 45-62 : 45-62

Yirrkala omanensis ( Norman, 1939)

Figs 3 C , 7 , Table 1

Sphagebranchus omanensis Norman, 1939 (type locality: Gulf of Oman).

Ichthyapus omanensis : Randall 1995: 61 (Gulf of Oman); Manilo and Bogorodsky 2003: S 95 (list, coast of Oman).

Yirrkala omanensis : McCosker 2022: 136 (Gulf of Oman).

Material examined.

• KMNH VR 100616 , 216 mm TL, Ke-tzu-liao , Kaohsiung, southwestern Taiwan, 6 March 2024, collected H. Kobayashi and Y. Hibino .

Diagnosis.

A relatively elongate species of Yirrkala with the following combination of characters: body reddish brown mostly except yellow tail end, with speckled patterns on head; SO 1 + 4; dorsal-fin origin well behind gill opening, slightly behind anus; lateral-line pores before anus 77; total vertebrae 140–141, MVF 77-76 - 141.

Description based on KMNH VR 100616 .

New record. Counts and measurements are shown in Table 1 . Body elongate, cylindrical, tip of tail laterally compressed and extremely pointed (Fig. 7 A ). Head moderate in size, 12.3 in TL; preanal length much longer than tail, 0.7 in tail length and 1.7 in TL.

Snout moderate in length, twice eye diameter, its tip weakly pointed; distinct median groove ventrally on snout but the groove opened completely, its anterior tip beyond anteriormost margin of first infraorbital pore; slope of dorsal surface of snout smooth, without notch or hump. Anterior nostril tubular but extremely short, tube length about half of pupil diameter; posterior nostril oval in shape with an inner valve, located on anteroventral margin of eye, opening ventrally. Eye moderate in size, covered by a transparent skin; center of eye anterior to mid-jaw (Fig. 7 B ). Interorbital region relatively narrow, weakly convex with an extremely shallow dimple (Fig. 7 C ). Mouth inferior, distance from tip of snout to anterior tip of lower jaw slightly shorter than twice eye diameter; lower jaw short, its tip relatively pointed and located anterior to a vertical through anterior margin of eye (Fig. 7 B, D ); rictus short, posterior end of gape well behind a vertical through posterior margin of eye; lips smooth with folds, the fold along upper lip weak, extending from a vertical through second infraorbital pore to posterior rictus; the fold along lower jaw short but obvious, extending from fourth mandibular pore to just before of first preopercular pore. Gill openings positioned ventrolaterally of breast close but not connected each side; shape of opening curved, diameter less than twice eye diameter.

Sensory pores on head developed, arrangement of those pores as follows (Fig. 3 C ): 1 (ethmoid) + 4 on supraorbital, 3 + 3 on infraorbital, 5 on lower jaw, 2 on preopercle, and 3 on supratemporal, one of those on mid-temporal; a single median interorbital pore. Lateral-line pores small but obvious. Lateral line almost complete except for near tip of tail, 8 anterior to a vertical through gill opening, 77 anterior to mid anus, 79 anterior to dorsal-fin origin, and total 136.

Teeth pointed, slightly recurved posteriorly; teeth on maxilla and dentary uniserial; teeth on vomer biserial irregularly anterior one-third and remaining uniserial; intermaxillary teeth slightly larger and more slender than maxillary teeth, three teeth arranged in a chevron shape along with edge of pre-ethmoid; intermaxillary teeth visible when mouth is closed.

Median fins very tiny and rudimental; origin of dorsal fin slightly behind that of anal fin, ending anterior to tip of tail about one snout length; origin of anal fin slightly behind anus, ending same as dorsal fin; caudal and pectoral fins absent.

Coloration. Just after captured (Fig. 7 ), body generally reddish brown, gradually changing to yellowish brown to brilliant yellow in posterior tail; numerous tiny melanophores covering dorsolateral body, ventral side without melanophores except tip of tail; numerous xanthophores also present including ventral side. Base color of head pale brown, coloring weaker than body; head with both melanophores and xanthophores, the former gathering and making speckles, arranged as a row along lips and postorbital region; pores on snout prominently margined, but others not margined necessarily, some connected with speckle. Dorsal and anal fins semitransparent white without darker margin. After preservation, brilliant yellow and red completely faded but all speckled remaining; transparent skin on eye becoming whitish.

Distribution.

Gulf of Oman (holotype) and southwestern Taiwan (this study). The Taiwanese specimen was estimated to be collected from a depth of around 10–50 m, based on the bycatches collected in the same haul.

Remarks.

Our specimen agrees well with the holotype in counts and body proportions (Table 1 ), as well as in the diagnostic feature of the speckles on head (Figs 7 , 8 ). The present specimen represents the second known specimen of Y. omanensis and the first record from the Pacific Ocean. This may suggest that Y. omanensis has a wide distribution in the Indo-West Pacific Ocean. However, additional specimens are needed to fully understand the complete distribution range of the species.

Yirrkala omanensis , originally Sphagebranchus omanensis , was described by Norman (1939) with a simple line drawing. McCosker (1977) suggested it is an incertae sedis, but subsequently, McCosker (2011) included it in Yirrkala without further explanation. Notably, this species is very unique in having the dorsal-fin origin situated far posterior, behind the anus, compared to a more anterior origin near the gill opening, such as in all other species of the genus except Y. insolitus . However, we agree with the McCosker’s (2011) taxonomic placement of this species in Yirrkala because all other characters of Y. omanensis are consistent with this genus.

Comparative materials.

Yirrkala kaupii : BMNH 1867.11. 28.304 (holotype), 342 mm TL, Manado, Sulawesi, Indonesia. Yirrkala lumbricoides : BMNH 1867.11. 28.322 (holotype), 229 mm TL, Timor, southern Malay Archipelago. Yirrkala misolensis : BMNH 1870.8. 31.112 (holotype), 280 mm TL, Misol Island, Irian Jaya, Indonesia. Yirrkala omanensis : BMNH 1939.5. 24.650 (holotype), 230 mm TL, Gulf of Oman. Yirrkala philippinensis : SU ( CAS) 30977 (holotype), 365 mm TL, Dumaguete, Oriental Negros, Philippines. Yirrkala tenuis : BMNH 1965.1. 2.1 (lectotype), no locality.

Figures

Figure 3. Line drawing of lateral head A Yirrkala nkust sp. nov., holotype, NMMB-P 38652, 496 mm TL B Yirrkala kaupii, NMMB-P 38424, 328 mm TL C Yirrkala omanensis, KMNH VR 100616, 216 mm TL. Arrows indicate ethmoid = 1 st supraorbital (lefts), interorbital (middles) and mid-temporal (rights) pores.

Figure 7. Fresh condition of Yirrkala omanensis, KMNH VR 100616, 216 mm TL, photographed by H. Kobayashi A whole body B lateral view of head C dorsal view of head D ventral view of head. AN anus DO dorsal-fin origin.

Figure 8. Holotype of Sphagebranchus omanensis, BMNH 1939.5. 24.650, 230 mm TL A whole body B lateral view of head C dorsal view of head D ventral view of head. All photos provided by Natural History Museum.